A Receive Pre-Amp you can build!

[Handy Andy]

Well, it already uses a dropping resistor off of D7 - if the AGC / PIN diode mod is the one you're talking about...

The 1.5K - has to be put in at D7 - anywhere else - the mod won't work as well...(D20 - Pin diode section) other sections feed voltage or take voltage from the line - it sums all of the voltages at or around D20 - D7 shares that trace line...

 

[Handy Andy]

Was doing some looking up of that D7 with 1.5K thingy - so I missed the later post you made...sorry 'bout that...

 

[TheRealPorkchop]

I’m talking about the one located about half way down the page listed as “super ears” here:
https://www.radiomods.co.nz/galaxy949_959ept069610z.html

 

[TheRealPorkchop]

Well the super ears thing is a novelty at best, hardly a real receive mod. I know from experience that it will increase what you hear but it’s also increasing noise and other useless junk. And it’s a real quick way to take out the front end if someone close hammers down on you.

I’m not terribly interested in it but kinda wanted to get it working in this radio as a nostalgic type thing. Trying to rebuild a radio I once I had from an almost impossible to polish turd radio.

 

[Handy Andy]

Read up on it - yeah, stay away from that mod if you want to keep your ears when you are running close to power from someone else. The Pin diodes can't save you - you'll need to add in more stuff than it's worth.

I'd just like to know what that pre-amp - hang-up - is about...

Need pics to help ya'

 

[Dmans]

Not sure if this will help, but here is a shot with the traces visible (?) and a shot with the component side visible. You can clearly see the transistor turned around from the silkscreen pattern.






73's
David

 

[Handy Andy]

All you had to do it just take a pic of the foil side - I got stuff over here that boss'll let me use to "merge" it

 

[Handy Andy]

The initial guesstimate and your "translucent" tends to agree with my first premise that the BCE and ECB issue but yours' works - so GAWD I hope all those little 1675's everyone's got, are proper pinouts...

 

[TheRealPorkchop]

Ok, I didn’t have any new 1675’s like I thought but I pulled two from a spare 3600 series board. The test ECB with the writing facing you on the transistor.

Pulled the one from the preamp, same configuration, ECB. And it shows good, no leakage.

 

[TheRealPorkchop]

Left this one out

Damn iPhone and it’s non-macro zooming lens camera setup crap.

 

[Handy Andy]

Yeppers, that's the one!

The new layout too - note the "bevel" versus the rounded silkscreen for the transistor outline- and yes, Base has all three coming into it. Even the lead traces are thicker - less loss to the etchant - and to me the better layout and built boards that can take the heat of the newer silver soldering and flux....

More than likely this board is not made for a Galaxy - too strong (signal boost) for it. Overloads L6 coil from signal. Probably "Saturates" the input and the radio tries to "clip" it off - see note below though - want to know the hookup and power routings you used.

So looks like this board won't work in your Galaxy - might work in weaker radio receivers that don't use a pre-selector setup like Galaxy has done. Will have to see - read below...

But at least we now have a "copy" template to work from and help others with.

And thank you for the confirmation of the ECB design, will trash that LGE PDF. Whew...Glad to know I didn't have a ton of rework on this simple little guy...

:Sorry to see this mod not work out for Galaxy radios using the 3600 boards...WOW...

One last question though... Where were you sourcing power from to power it?

 

[TheRealPorkchop]

I removed C43 and first put the green wire in side going to the coil, have to go look at the radio to give a slot location. Then the yellow wire went in the side closer to L33 or in that direction. This is all with the radio face towards me and the parts side up. I got nothing so I reversed the wires, still nothing.

I hooked the ground and power directly to the power socket inside the radio.

 

[Handy Andy]

Ahh, ok, hmmm-well it is labeled as such...wonder if - instead - it self - oscillated and overloaded the front end - there is little there to keep it stable...oscillates at it's own frequency.

So...I wonder if the 13.8 is TOO much for it - there is very little bypassing to keep itself to itself - and from not interacting with the other parts...so do we need to find a cleaner power source?

There may also be a need for it's input to be from a TUNED source - aka coil - hard to do that with a Galaxy - you already have the RF amp and no preselector except for L6 so you're already at the right spot to put it in.

Else - power feed issues - long wire runs poor noisy grounds - stuff like that...that means lead dress too...

Thinking R6 - that 100 ohm the feeds the RF amp TR17 - but you have to pull it from the undropped side - the side straight off the power feed. IF you take power from the wrong side of that resistor - it'll kill the circuit by loading it down too much. So, we need some fresh breath of air to feed it. So that means a clean shot to the RX power. The one that is the switched side of TR36 RX power that feds the RX strip. It's 8 volts but it also has some bypassing so it should be pretty clean.

These may just be shots in the dark, so that means- take them for what it's worth -

At least you tried - thanks!

:+> Andy <+:

 

[TheRealPorkchop]

Well, I can try powering it with a variable supply, I’ll start at 8v and see what happens. I have a pile of other radios in the shop I can try it in, I’ll try that as well.

My original intention of buying them was for experimenting anyway and I thought maybe they’d work for adding into amps for a good preamp. That’s something I’d really like to find, a good preamp to add into amps that don’t have one. The problem I’ve seen is what’s been said already, most of them add noise instead of just the signal.

 

[TheRealPorkchop]

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/202408450412

What about that do-hickey? Thoughts?